The present invention relates to adaptive error concealment, and more particularly, to such concealment that uses information from adjacent lines to determine the method of concealment.
Prior U.S. application Ser. No. 241,925, filed Mar. 9, 1981, entitled "Interleaved Recording Format For digital Video", and assigned to the assignee of the present invention, now U.S. Pat. No. 4,393,414, describes a method of formatting component video data on tape so that a dropout affects every other pixel on a given television line, and if a dropout is of long duration, it affects pixels on an interleaved basis on adjacent TV lines. FIG. 1 shows such an error pattern for a dropout of at least three lines duration, after the original sequential order of the pixels is restored, and wherein X and O respectively denote erroroneous and correct pixels. This format arrangement is ideal for a two-track DVTR (Digital Video Tape Recorder) since it is easily implementable; however, the error pattern of every other sample in error imposes a difficult situation for error concealment. One approach to concealing an erroneous pixel would be to average the four correct pixels (that is, top, bottom, left and right) surrounding the good pixel. Consider the data shown in FIG. 2, which shows an error pattern for either a long or short (less than one line) dropout. Here the pixels above and below the erroneous pixel are white, while the pixels to the left and right are black. This pattern could occur from a single horizontal black line on a white field, in which case the correct value for the erroneous pixel is black, or from vertical black and white stripes having a high frequency, in which case the correct value for the erroneous pixel is white. Averaging the four pixels provides a replacement pixel that is grey, which is not a good replacement value in either case.
Adaptive techniques based on a minimum difference criterion have been described in prior U.S. application Ser. No. 170,811, filed July 21, 1980, entitled "Two-Dimensional Adaptive Dropout Compensator and Chroma Inverter", now U.S. Pat. No. 4,376,955, and assigned to the assignee of the present application. In such a technique the amount of change (difference) of the video signal in at least two directions is computed, and averaging to produce a replacement pixel is done in the direction having the least amount of change. However, in the case of high resolution component video, these techniques also run into difficulty. Consider the previous example shown in FIG. 2. The pixels above and below are both white, and thus the vertical difference is zero. The left and right pixels are both black, and thus the horizontal difference is also zero. Thus, in this case, minimum differencing provides no information for selecting which average (horizontal or vertical) to use as the replacement pixel, and the wrong average may be selected.
It is therefore desirable to provide a more accurate error concealment system.